Timing adjustment method in a mobile communication system that performs an adjustment of uplink transmission timing by random access between a user equipment and a base station

ABSTRACT

A mobile communication system having a user equipment that performs transmission process having transmission timing adjustment information and a base station that receives a signal sent from the user equipment, the mobile communication system includes, if a timer controlling a term of application of first transmission timing adjustment information expires before transmission of a signal including identification information of the user equipment is performed during a connection process including reception of second transmission timing adjustment information while the user equipment has the first transmission timing adjustment information and performing the connection process to the base station, the user equipment does not transmit the signal.

CROSS-REFERENCE TO RELATED APPLICATION

This present Application is a Divisional Application of U.S. applicationSer. No. 12/957,478, filed on Dec. 1, 2010, now pending, which is aContinuation of International Application No. PCT/JP2008/060151 filed onJun. 2, 2008 in Japan, the contents of each are herein whollyincorporated by reference. The present Application also relates to U.S.application Ser. No. 13/079,265, filed Apr. 4, 2011, now pending.

FIELD

The present disclosure related to a timing adjustment method, a userequipment, a base station, and a mobile communication system. Thepresent disclosure may be used for control uplink (UL) communications ina wireless (mobile) communication system.

BACKGROUND

Currently, third-generation mobile communication services by means ofthe code division multiple access (CDMA) scheme have just introduced inwireless (mobile) communication systems, including wireless terminals(user terminals), such as cellular phones. At the same time,next-generation mobile communication technologies capable of providingeven faster communications have been under development. The 3rdGeneration Partnership Project (3GPP) is studying the Long TermEvolution (LTE), as one of such next-generation mobile communicationtechnologies.

In a mobile communication system, as a preparation to a wireless basestation (evolved Node B: eNB) and a user terminal (user equipment: UE)for initiating a communication with each other, a channel is providedfor the UE to initiate a transmission to the eNB. The 3GPP refers thischannel as a “random access channel (RACH)”, and refers the procedurefor initiating a communication through an RACH as a “random access(RA)”.

Random accesses in the LTE are designed in a Slotted Aloha model,wherein a time and frequency resources for sending an RACH are reserved.An RACH contains information, using which the eNB distinguishes UEs fromeach other which make transmissions. In other words, in order to sharean RACH among a plurality of UEs, an identifier called a signature (orpreamble) is included.

The respective UEs perform transmission using one signature of aplurality of candidate signatures. Thus, even if the different UEs sendsignatures via the RACH using the same time and frequency resource, theeNB can distinguish between the UEs based on the received signatures aslong as the respective UE employ different signatures.

The RACH is used when initiating a communication, and individualchannels (or shared channels) are used afterwards.

A UE make an RA, for example, upon an initial transmission(origination), in response to an incoming transmission from the eNB(generation of downlink (DL) data), upon handover, upon recovery fromdisconnection (resuming a disconnected communication). As used herein, awireless link in the direction from the eNB to a UE is referred to as“downlink (DL)”, and a wireless link in the opposite direction as“uplink (UL)”.

There may be some cases wherein an eNB does not recognize some UEs uponan initial transmission or recovery from disconnection, for example, andno individual signatures that can be exclusively used are allocated tothe UEs. Such UEs select one of a plurality of (for example, 64) presetsignatures for making an RA. Accordingly, a plurality of UEs maysimultaneously make RAs using the same signature, although thepossibility of such an event is low. Such an RA procedure is referred toas a “contention based random access procedure (contention based RAprocedure).

In such a case, the eNB resolves the conflicted signature (select one ofthe competing UEs), and sends a response to the selected UE. Each UEdetermines that UE is selected by the eNB whether a response is receivedfrom the eNB. The UE selected by the eNB continues the communication (RAprocedure) with the eNB, makes settings for the wireless channel withthe eNB, and so on. The UE that was not selected by the eNB tries toretry an RA after a predetermined time interval or otherwise.

Note that such a contention of a signature occurs while a UE makes ahandover to switch between eNBs for connecting, the connection might betemporarily disconnected or sometimes a communication might bedisconnected. For this purpose, the LTE proposes to allocate individualsignatures in advance to each of UEs for making a handover. Such an RAprocedure is referred to as “non-contention based random accessprocedure (non-contention based RA procedure)”.

-   Non-Patent Document 1: 3GPP TS 36.321 V8.1.0; “Evolved Universal    Terrestrial Radio Access (E-UTRA); Medium Access Control (MAC)    protocol specification”, searched online on May 22, 2008, on the    Internet; URL: http://www.3gpp.org/ftp/Specs/html-info/36321.htm

SUMMARY Problems to be Solved by the Invention

Conventionally, inconvenience of adjustment of transmission timing maybe experienced during a RA (during execution thereof), due to expirationof information for adjusting the transmission timing.

SUMMARY

For example, the following aspects are used:

(1) A timing adjustment method in a mobile communication system having auser equipment that performs transmission processing based ontransmission timing adjustment information and a base station thatreceives a signal sent from the user equipment, including: in responseto receiving second transmission timing adjustment information duringconnection processing while the user equipment is performing theconnection processing to the base station based on first transmissiontiming adjustment information, applying the first transmission timingadjustment information to transmission timing adjustment fortransmission processing until a valid term of the first transmissiontiming adjustment information; and applying the second transmissiontiming adjustment information to transmission timing adjustment fortransmission processing after the valid term of the first transmissiontiming adjustment information, may be used.

(2) A timing adjustment method in a mobile communication system having auser equipment that performs transmission processing based ontransmission timing adjustment information and a base station thatreceives a signal sent from the user equipment, including: includingsecond transmission timing adjustment information in a signal includingidentification information of the user equipment that is sent from thebase station to the user equipment during connection processing whilethe user equipment is performing the connection processing to the basestation based on first transmission timing adjustment information, maybe used.

(3) A timing adjustment method in a mobile communication system having auser equipment that performs transmission processing based ontransmission timing adjustment information and a base station thatreceives a signal sent from the user equipment, including: in responseto receiving second transmission timing adjustment information duringconnection processing while the user equipment is performing theconnection processing to the base station based on first transmissiontiming adjustment information, continuing to apply the firsttransmission timing adjustment information without applying the secondtransmission timing adjustment information and extending a valid term ofthe first transmission timing adjustment information, may be used.

(4) A timing adjustment method in a mobile communication system having auser equipment that performs transmission processing based ontransmission timing adjustment information and a base station thatreceives a signal sent from the user equipment, including: if a validterm of first transmission timing adjustment information expires beforetransmission processing of a signal including identification informationof the user equipment is performed during connection processing whilethe user equipment is performing the connection processing to the basestation based on the first transmission timing adjustment information,performing the transmission processing of the signal based on the firsttransmission timing adjustment information, may be used.

(5) A timing adjustment method in a mobile communication system having auser equipment that performs transmission processing based ontransmission timing adjustment information and a base station thatreceives a signal sent from the user equipment, including: if a validterm of first transmission timing adjustment information expires beforetransmission processing of a signal including identification informationof the user equipment is performed during connection processing whilethe user equipment is performing the connection processing to the basestation based on the first transmission timing adjustment information,aborts the connection processing, may be used.

(6) A timing adjustment method in a mobile communication system having auser equipment that performs transmission processing based ontransmission timing adjustment information and a base station thatreceives a signal sent from the user equipment, including: if the userequipment sends a signal including identification information of theuser equipment during connection processing while the user equipment isperforming the connection processing to the base station based on firsttransmission timing adjustment information and the base station receivesthe signal, sending, by the base station, second transmission timingadjustment information to the user equipment, in response to thereceiving the signal, may be used.

(7) A user equipment in a mobile communication system having the userequipment and a base station that receives a signal sent from the userequipment, including: a transmission processing unit that performstransmission processing on the base station based on transmission timingadjustment information; and a control unit that, in response toreceiving second transmission timing adjustment information duringconnection processing by the transmission processing unit while the userequipment is performing the connection processing to the base stationbased on first transmission timing adjustment information, applies thefirst transmission timing adjustment information to transmission timingadjustment for transmission processing until a valid term of the firsttransmission timing adjustment information, and applies the secondtransmission timing adjustment information to transmission timingadjustment for transmission processing by the transmission processingunit after the valid term of the first transmission timing adjustmentinformation, may be used.

(8) A base station in a mobile communication system having a userequipment that performs transmission processing based on transmissiontiming adjustment information and the base station that receives asignal sent from the user equipment, including: a control unit thatincludes second transmission timing adjustment information in a signalincluding identification information of the user equipment that is sentto the user equipment during connection processing while the userequipment is performing the connection processing to the base stationbased on first transmission timing adjustment information, may be used.

(9) A user equipment in a mobile communication system having the userequipment and a base station that receives a signal sent from the userequipment, including: a transmission processing unit that performstransmission processing on the base station based on transmission timingadjustment information; and a control unit that, in response toreceiving second transmission timing adjustment information duringconnection processing while performing the connection processing to thebase station based on first transmission timing adjustment information,continues to apply the first transmission timing adjustment informationwithout applying the second transmission timing adjustment informationand extends a valid term of the first transmission timing adjustmentinformation, may be used.

(10) A user equipment in a mobile communication system having the userequipment and a base station that receives a signal sent from the userequipment, including: a transmission processing unit that performstransmission processing on the base station based on transmission timingadjustment information; and a control unit that, if a valid term offirst transmission timing adjustment information expires beforetransmission processing of a signal including identification informationof the user equipment is performed during connection processing whileperforming the connection processing to the base station based on thefirst transmission timing adjustment information, performs thetransmission processing of the signal based on the first transmissiontiming adjustment information, may be used.

(11) A user equipment in a mobile communication system having the userequipment and a base station that receives a signal sent from the userequipment, including: a transmission processing unit that performstransmission processing on the base station based on transmission timingadjustment information; and a control unit that, if a valid term offirst transmission timing adjustment information expires beforetransmission processing of a signal including identification informationof the user equipment is performed during connection processing whileperforming the connection processing to the base station based on thefirst transmission timing adjustment information, aborts the connectionprocessing, may be used.

(12) A base station in a mobile communication system having a userequipment that performs transmission processing based on transmissiontiming adjustment information and the base station that receives asignal sent from the user equipment, including: a reception processingunit that receives a signal sent from the user equipment; and a controlunit that, if the reception processing unit receives a signal includingidentification information of the user equipment during connectionprocessing while the user equipment is performing the connectionprocessing to the base station based on first transmission timingadjustment information and the base station receives the signal, sendssecond transmission timing adjustment information to the user equipment,in response to the receiving the signal, may be used.

(13) A mobile communication system having a user equipment that performstransmission processing based on transmission timing adjustmentinformation and a base station that receives a signal sent from the userequipment, wherein the system in response to receiving secondtransmission timing adjustment information during connection processingwhile the user equipment is performing the connection processing to thebase station based on first transmission timing adjustment information,applies the first transmission timing adjustment information totransmission timing adjustment for transmission processing until a validterm of the first transmission timing adjustment information; andapplies the second transmission timing adjustment information totransmission timing adjustment for transmission processing after thevalid term of the first transmission timing adjustment information, maybe used.

(14) A mobile communication system having a user equipment that performstransmission processing based on transmission timing adjustmentinformation and a base station that receives a signal sent from the userequipment, wherein the user equipment includes second transmissiontiming adjustment information in a signal including identificationinformation of the user equipment that is sent from the base station tothe user equipment during connection processing while the user equipmentis performing the connection processing to the base station based onfirst transmission timing adjustment information, may be used.

(15) A mobile communication system having a user equipment that performstransmission processing based on transmission timing adjustmentinformation and a base station that receives a signal sent from the userequipment, wherein in response to receiving second transmission timingadjustment information during connection processing while the userequipment is performing the connection processing to the base stationbased on first transmission timing adjustment information, the userequipment continues to apply the first transmission timing adjustmentinformation without applying the second transmission timing adjustmentinformation and extends a valid term of the first transmission timingadjustment information, may be used.

(16) A mobile communication system having a user equipment that performstransmission processing based on transmission timing adjustmentinformation and a base station that receives a signal sent from the userequipment, wherein if a valid term of first transmission timingadjustment information expires before transmission processing of asignal including identification information of the user equipment isperformed during connection processing while the user equipment isperforming the connection processing to the base station based on thefirst transmission timing adjustment information, the user equipmentperforms the transmission processing of the signal including theidentification information of the user equipment based on the firsttransmission timing adjustment information, may be used.

(17) A mobile communication system having a user equipment that performstransmission processing based on transmission timing adjustmentinformation and a base station that receives a signal sent from the userequipment, wherein if a valid term of first transmission timingadjustment information expires before transmission processing of asignal including identification information of the user equipment isperformed during connection processing while the user equipment isperforming the connection processing to the base station based on thefirst transmission timing adjustment information, the user equipmentaborts the connection processing, may be used.

(18) A mobile communication system having a user equipment that performstransmission processing based on transmission timing adjustmentinformation and a base station that receives a signal sent from the userequipment, wherein if the user equipment sends a signal includingidentification information of the user equipment during connectionprocessing while the user equipment is performing the connectionprocessing to the base station based on first transmission timingadjustment information and the base station receives the signal, thebase station sends second transmission timing adjustment information tothe user equipment, in response to the receiving the signal, may beused.

The object and advantages of the embodiment will be realized andattained by means of the elements and combinations particularly pointedout in the claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and arenot restrictive of the embodiment, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating one example of a wireless(mobile) communication system in accordance with a first embodiment.

FIG. 2 is a sequence diagram illustrating one example of a contentionbased RA procedure;

FIG. 3 is a flowchart illustrating an example of the operation of a UEin the contention-based RA procedure;

FIG. 4 is a flowchart illustrating an example of the operation of an eNBin the contention-based RA procedure;

FIG. 5 is a sequence diagram illustrating one example of a ULcommunication control (technique 1-1) according to a first embodiment;

FIG. 6 is a sequence diagram illustrating another example of a ULcommunication control (technique 1-1) according to the first embodiment;

FIG. 7 is a sequence diagram illustrating another example of a ULcommunication control (technique 1-1) according to the first embodiment;

FIG. 8 is a flowchart illustrating one example of a UL communicationcontrol (technique 1-1) by a UE according to a first embodiment;

FIG. 9 is a sequence diagram illustrating one example of a ULcommunication control (technique 1-2) according to a first embodiment;

FIG. 10 is a sequence diagram illustrating another example of a ULcommunication control (technique 1-2) according to the first embodiment;

FIG. 11 is a sequence diagram illustrating another example of a ULcommunication control (technique 1-2) according to the first embodiment;

FIG. 12 is a flowchart illustrating one example of a UL communicationcontrol (technique 1-2) by a UE according to a first embodiment;

FIG. 13 is a sequence diagram illustrating one example of a ULcommunication control (technique 1-3) according to a first embodiment;

FIG. 14 is a sequence diagram illustrating another example of a ULcommunication control (technique 1-3) according to the first embodiment;

FIG. 15 is a sequence diagram illustrating another example of a ULcommunication control (technique 1-3) according to the first embodiment;

FIG. 16 is a flowchart illustrating one example of a UL communicationcontrol (technique 1-3) by a UE according to a first embodiment;

FIG. 17 is a sequence diagram illustrating one example of a ULcommunication control (technique 1-4) according to a first embodiment;

FIG. 18 is a sequence diagram illustrating another example of a ULcommunication control (technique 1-4) according to the first embodiment;

FIG. 19 is a sequence diagram illustrating another example of a ULcommunication control (technique 1-4) according to the first embodiment;

FIG. 20 is a flowchart illustrating one example of a UL communicationcontrol (technique 1-4) by a UE according to a first embodiment;

FIG. 21 is a sequence diagram illustrating one example of a ULcommunication control (technique 2-1) according to a second embodiment;

FIG. 22 is a sequence diagram illustrating another example of a ULcommunication control (technique 2-1) according to the secondembodiment;

FIG. 23 is a sequence diagram illustrating another example of a ULcommunication control (technique 2-1) according to the secondembodiment;

FIG. 24 is a flowchart illustrating one example of a UL communicationcontrol (technique 2-1) by a UE according to the second embodiment;

FIG. 25 is a sequence diagram illustrating one example of a ULcommunication control (techniques 2-2 and 2-3) according to the secondembodiment;

FIG. 26 is a sequence diagram illustrating another example of a ULcommunication control (techniques 2-2 and 2-3) according to the secondembodiment;

FIG. 27 is a sequence diagram illustrating another example of a ULcommunication control (techniques 2-2 and 2-3) according to the secondembodiment;

FIG. 28 is a flowchart illustrating one example of a UL communicationcontrol (technique 2-2) by a UE according to the second embodiment;

FIG. 29 is a flowchart illustrating one example of a UL communicationcontrol (technique 2-3) by a UE according to the second embodiment;

FIG. 30 is a sequence diagram illustrating one example of a ULcommunication control (technique 2-4) according to the secondembodiment;

FIG. 31 is a sequence diagram illustrating another example of a ULcommunication control (technique 2-4) according to the secondembodiment;

FIG. 32 is a sequence diagram illustrating another example of a ULcommunication control (technique 2-4) according to the secondembodiment;

FIG. 33 is a flowchart illustrating one example of a UL communicationcontrol (technique 2-4) by a UE according to the second embodiment;

FIG. 34 is a sequence diagram illustrating one example of a ULcommunication control (technique 3-3) according to a third embodiment;

FIG. 35 is a sequence diagram illustrating another example of a ULcommunication control (technique 3-3) according to the third embodiment;

FIG. 36 is a flowchart illustrating one example of a UL communicationcontrol (technique 3-3) by an eNB according to the third embodiment; and

FIG. 37 is a flowchart illustrating one example of a UL communicationcontrol (technique 3-3) by a UE according to the third embodiment.

DESCRIPTION OF EMBODIMENTS

Hereunder is a description of embodiments with reference to thedrawings. Note that the embodiments that will be described are merelyexemplary, and it is not intended to exclude various variations andapplications of techniques that are not described. In other words, thepresent embodiments can be practiced in various ways (by combiningexamples, for example) without departing from the spirit thereof.

(1) First Embodiment

FIG. 1 is a block diagram illustrating one example of a wireless(mobile) communication system in accordance with a first embodiment. Thesystem depicted in FIG. 1 includes an the eNB 10 as one example of awireless base station, and a UE 20 that may communicate with the eNB 10via a wireless link in a wireless area of the eNB 10, as one example ofa wireless terminal (user equipment).

Although one eNB 10 and one UE 20 are illustrated in FIG. 1, a pluralityof eNBs 10 and UEs 20 may be present in this wireless communicationsystem. The wireless link includes DL and UL wireless channels. Each ofthe DL and UL wireless channels may include a shared channel shared bymultiple UEs and individual channels exclusively used by the respectiveUEs.

In addition, the same configurations of the eNB 10 and the UE 20depicted in FIG. 1 may be used in second to third embodiments that willbe described below. Furthermore, the wireless base station 10 in thisembodiment is considered as an eNB of the LTE having a some or all ofthe functions of a radio network controller (RNC), the wireless basestation 10 may be any other base station in older generations than theLTE (without the functions of the RNC). In addition, the wireless basestation 10 may be any base station in any other system in which an RAprocedure is defined.

(1.1) Description of eNB

The eNB 10 may include a transceiver antenna 11, a transceiver unit 12,a buffer 13, a UL synchronization determination unit 14, a timermanagement unit 15, and a UL resource management unit 16.

The transceiver antenna 11 (hereinafter, it may be simply referred to as“antenna 11”) sends a DL wireless signal which in turn may be receivedby the UE 20 located within a wireless area (cell or sector) serviced bythe eNB 10, as well as receiving a UL wireless signal sent by the UE 20.

The transceiver unit 12 executes predetermined transmission processingon transmission data addressed to the UE 20 (including user data,control data, and the like) to generate a wireless channel signal, andoutputs the signal to the transceiver antenna 11. Examples of thetransmission processing may include encoding of the DL transmissiondata, modulation of the encoded data, mapping of the modulated signal toa frame in a predetermined channel, frequency conversion (upconversion)of the frame signal into a wireless frequency, power amplification ofthe wireless frame. The wireless frame may be a wireless frame based onthe Orthogonal Frequency Division Multiplexing (OFDM) or OrthogonalFrequency Division Multiple Access (OFDMA), for example.

The transceiver unit 12 executes predetermined reception processing on aUL wireless signal (wireless frame) received by the antenna 11 to obtainUL data (including user data, control data, and the like) sent by the UE20. Examples of the reception processing may include low-noiseamplification of the received signal, frequency conversion(downconversion) to the baseband frequency, gain adjustment,demodulation, and decoding. Note that the transceiver unit 12 may bedivided into a transmitter unit and receiver unit, based on thefunctions.

The buffer unit 13 temporarily retains UL reception data and/or DLtransmission data.

The timer management unit 15 generates a TA (time alignment) value asone example of transmission timing adjustment information that isperiodically sent (notification) to the UE 20 for ensuring (maintaining)UL synchronization. Generation and notification of the TA value isperformed for a UE 20 for which a call is set and a wireless resource(UL resource) is allocated which is used by the UE 20 for sending ULdata.

TA value is one type of control information used for adjusting(synchronizing) the timing of transmission of UL data by the UE 20 andthe timing of the reception timing of the UL data by the eNB 10. Inother words, the TA value is used to adjust the UL transmission timingby a UE 20 such that reception processing is performed by thetransceiver unit 12 at appropriate timing. Accordingly, the UE 20 canensure UL synchronization by adjusting UL transmission timing inaccordance with the TA value received from the eNB 10.

Since a UE 20 may not remain in the same location, TA values arevariable in accordance with the distance between the eNB 10 and the UE20 (location of the UE 20). Hence, in order for the UE 20 to ensure(maintaining) UL synchronization, it is desirable to periodically updatethe TA value.

As one example for achieving such updating, the eNB 10 periodicallygenerates a TA value in accordance with the location of a UE 20 andnotifies the UE 20 of it. A DL control signal used for such anotification is referred to as a “TA command”. The eNB 10 can locate aUE 20 using a UL control signal received from that UE 20. The controlsignal used for this measurement may be a known signal, such as an SRS(sounding reference signal), for example.

In addition, the timer management unit 15 also includes a ULsynchronization timer (TA timer 151). The TA timer 151 is started inresponse to a TA value being send (notified) to a UE 20. The timermanagement unit 15 monitors this timer value. Since a UE 20 may movesand thus changes its location, a TA value that has been notified to theUE 20 becomes invalid in some point in time. Accordingly, the valid termof a TA value that was notified to a UE 20 is monitored using the TAtimer 151. The TA timer 151 is restarted every time a new TA value isgenerated and notified.

The UL synchronization determination unit (control unit) 14 monitors theTA timer 151 (timer value), and determines whether or not ULsynchronization has been established (maintained) for receiving UL dataor for receiving an acknowledgement in the UL after sending DL data. Forexample, if the TA timer 151 expires (is timed out), it is determinedthat the UL synchronization has been lost even if UL synchronization isactually (in a lower layer) established (maintained).

The UL resource management unit 16 manages UL resources used for ULcommunications (including communications during an RA) with UEs 20, suchas channel frequencies and time (transmission and reception timings),for example, and also manages allocation and deallocation of suchresources. When a format for the OFDMA scheme is adopted for a wirelessframe, the management of the wireless resource includes management ofplacement (mapping) of two-dimensional transmission and receptionregions (referred to as “bursts”) defined by subchannel frequencies andsymbol times.

Such UL resources may include UL control channels (PUCCHs: PhysicalUplink Control Channels) that individualized for respective UEs 20, andresources of SRSs used by the eNB 10 for channel estimation and locatingUEs 20. In addition, PUCCH resources include resources used by UEs 20for sending CQI (Channel Quality Information) or SRIs (SchedulingRequest Indicators) to the eNB 10.

A CQI resource is used for reporting the reception status (quality) at aUE 20 to the eNB 10. The eNB 10 can adaptively control DL transmission(such as the amount of data to be sent, the modulation scheme, the coderate) based on the CQI received from the UE 20.

An SRI resource is used by a UE 20 for informing the eNB 10 that UL datato be sent has been generated at the UE 20 if UL synchronization isestablished. A UE 20 which has no SRI resource allocated to that UE 20can inform generation of UL data to the eNB 10 by performing an RA. A UE20 that has not established UL synchronization yet can inform the eNB 10of generation of UL data by performing an RA.

The UL resource management unit 16 is allowed to deallocate a PUCCHresource (CQI resource, SRI resource) and an SRS resource that have beenallocated to a UE 20 when the TA timer 151 is timed out.

(1.2) Description of UE

In contrast, a UE 20 depicted in FIG. 1 may include a transceiverantenna 21, a transceiver unit 22, a buffer 23, a UL synchronizationdetermination unit 24, a timer management unit 25, and a UL resourcemanagement unit 26.

The transceiver antenna 21 (hereinafter, it may be simply referred to as“antenna 21”) sends a UL wireless signal to the eNB 10 in a wirelessarea (cell or sector) serviced by the eNB 10, as well as receiving a DLwireless signal sent by the eNB 10.

The transceiver unit 22 executes predetermined transmission processingon UL transmission data addressed to the eNB 10 (including user data,control data, and the like) to generate a wireless channel signal, andoutputs the signal to the transceiver antenna 21. Examples of thetransmission processing may include encoding of the UL transmissiondata, modulation of the encoded data, mapping of the modulated signal toa frame in a predetermined channel, frequency conversion (upconversion)of the frame signal into a wireless frequency, power amplification ofthe wireless frame.

The transceiver unit 22 executes predetermined reception processing on aDL wireless signal (wireless frame) received by the antenna 21 to obtainDL data (including user data, control data, and the like) sent by theeNB 10. Examples of the reception processing may include low-noiseamplification of the received signal, frequency conversion(downconversion) to the baseband frequency, gain adjustment,demodulation, and decoding. Note that the transceiver unit 22 may bedivided into a transmitter unit and receiver unit, based on thefunctions.

The buffer unit 23 temporarily retains UL transmission data and/or DLreception data.

The timer management unit 25 includes a UL synchronization timer (TAtimer) 251 that is similar to the corresponding timer in the eNB 10, andmonitors the valid term of the TA value by managing (monitoring) thetimer value thereof. The TA timer 251 is started or restarted inresponse to a TA command being received from the eNB 10. If a new TAvalue is receive from the eNB 10 during a contention-based RA procedure(connection processing), it is possible to rely on the TA value of a TAcommand received from the eNB 10 before starting the RA procedure. Inthis case, ignoring a TA value received during the RA procedure ispermitted, and any control wherein the TA timer 251 is not restarted isallowed. In addition, the timer management unit 25 includes a memory252, and stores a TA value received from the eNB 10 during the RAprocedure may be stored in the memory 252 for future use.

The UL synchronization determination unit (control unit) 24 monitors theTA timer 251 (timer value), and determines whether or not ULsynchronization has been established (maintained). If the TA timer 251is timed out, it is determined that the UL synchronization has beenlost. Accordingly, if a TA value received from the eNB 10 is ignoredduring an RA procedure, the TA timer 251 is timed out, which may resultin determination that synchronization has been lost during the RAprocedure.

The UL resource management unit 26 manages UL resources allocated fromthe eNB 10, and manages disallocation of such resources. If the TA timer251 is timed out and thus the UL synchronization determination unit 24determines that synchronization has been lost, the UL resourcemanagement unit 26 is allowed to be deallocated an allocated ULresource.

(1.3) Contention-based RA procedure

Hereinafter, a contention-based RA procedure as one example offundamental connection processing between an eNB 10 and a UE 20 asdescribed above will be described with reference to FIG. 2 to FIG. 4.FIG. 2 is a sequence diagram illustrating one example of a contentionbased RA procedure. FIG. 3 is a flowchart illustrating one example of acontention-based RA procedure at the UE 20, and FIG. 3 is a flowchartillustrating one example of a contention-based RA procedure at the eNB10.

A contention-based RA procedure is performed UL data to be sent isgenerated in the UE 20 (initial transmission by the UE 20), or when DLdata directed to the UE 20 arrives at the eNB 10 and an incomingnotification of the DL data is received from the eNB 10. The flowchartin FIG. 3 indicates the former scenario while the flowchart in FIG. 4indicates the latter scenario.

As illustrated in FIG. 3, once UL data is generated in the UE 20, the UE20 determines, by the UL synchronization determination unit 24, whetheror not UL synchronization has been established (Processing 1101 toProcessing 1103).

If it is determined that UL synchronization has not been established yet(if “no” in Processing 1103), the UE 20 selects one of a plurality ofsignatures (preambles) that have been provided by the UL resourcemanagement unit 26. This selection is made for the purpose of minimizingthe possibility of the same signature being selected by multiple UEs,and a variety of selection schemes may be employed, such as bygenerating a random number and make a selection based on the randomnumber. The selected signature is included in a message #1 (included inan RA preamble), and is sent from the transceiver unit 22 to the eNB 10on an RACH (Processing 1011 in FIG. 2 and Processing 1104 in FIG. 3).

In response to receiving the message #1, the eNB 10 sends a responsemessage #2 (RA response) to that message, to the UE 20 (Processing 1012in FIG. 2). This RA response #2 may include identifier(s) of one or moresignatures which have been received (identified) by the eNB 10,transmission grants for the shared UL channel corresponding to thesignatures, and an identifier temporarily allocated for identifying adestination (UE 20) in subsequent RA communications. This identifier isreferred to as a “temporary-connection radio network temporaryidentifier (T-CRNTI)”.

In response to receiving the RA response #2 from the eNB 10 (Processing1105 in FIG. 3), the UE 20 checks whether or not the signature that wassent in the message #1 is contained in the received information.

When it is contained, the UE 20 sends (scheduled transmission) a message#3 based on the transmission grant that is contained in the RA response#2 and corresponds to the signature which the UE 20 sent (Processing1013 in FIG. 2 and Processing 1106 in FIG. 3). The message #3 is asignal containing scheduling request to the eNB 10, and may include asystem architecture evolution (SAE)—temporary mobile subscriber identity(S-TMSI) as one example of the identification number of the UE 20.

The UE 20 selects a signature in the message #1, and it is possible thatmultiple UEs 20 simultaneously send messages #1 to the eNB 10 using thesame signature.

In such as case, although the eNB 10 cannot distinguish the UEs 20 fromeach other, the eNB 10 can identify the UEs 20 causing the contention ofthe signature by using received identification numbers (S-TMSIs) sentfrom the UEs 10 in the message 3. Accordingly, the eNB 10 can selectsone of the UEs 20, thereby resolving the contention. The selection maybe based on the received field intensities of the messages #1. Forexample, the eNB 10 selects one UE 20 that has the strongest receivedfield intensity of the message #1.

The eNB 10 sends a message #4 (Contention Resolution) to the UE 20selected in the contention resolution (Processing 1014 in FIG. 2). Thismessage #4 may include information sent in the message #3, such as theS-TMSI.

In response to receiving the message #4 from the eNB 10 (Processing 1107in FIG. 3), the UE 20 checks whether there is any contention with otherUEs 20 (checks whether or not its own identification information isincluded or not) (Processing 1108 in FIG. 3), and the UL connectionprocessing is completed if there is no contention (the “no” route fromProcessing 1108 in FIG. 3). After this step, the UE 20 employs thetemporary identifier (T-CRNTI) that was temporarily allocated forcommunications with the eNB 10, as non-temporary identifier(C(cell)-RNTI).

Otherwise, if it is confirmed that there is contention with other UE(s)20 as a result of receiving the message #4 (if its own identificationinformation is not included) (“yes” in Processing 1108), that UE 20waits for a time period specified in a backoff (Processing 1111). Here,the “backoff” refers to information specifying the timing for the UE 20to retry a contention-based RA procedure (waiting time period).

The parameter of the backoff is notified in the message #2, and usingdifferent values of the backoff for respective UEs 20 can significantlyreduce the possibility of another contention upon retrying. Morespecifically, the maximum of the backoff time is notified in the message#2, and a UEs 20 calculate backoff time in this range. For calculatingthe backoff time, various techniques may be employed, such as using arandom number.

The UE 20 then checks whether or not a maximum retry count is reached bya retry of a further next RA procedure (Processing 1112). If the maximumretry count is not reached (if “no” in Processing 1112), the UE 20retries RA procedure by performing Processing 1103 and subsequent steps(sends a message #1). If the maximum retry count is reached (if “yes” inProcessing 1112), the UE 20 notifies the upper layer of this fact(Processing 1113). The upper layer is a radio resource control (RRC)layer that belongs to the layer 3, for example.

In response to the notification, the upper layer starts a monitor timerthat monitors if RA continues (is retried). If this monitor timer istimed out, the upper layer of the UE 20 performs a control forreselecting an eNB 10 (cell) to which a UL connection request is to besent (a message #1 is to be sent) (cell selection control or cellreselection control).

Note that if UL synchronization has been established in Processing 1103,(if “yes” in Processing 1103), the UE 20 checks whether or not a PUCCHresource (SRI resource) has been allocated (Processing 1109). If so (if“yes” in Processing 1109), the UE 20 sends an SRI (transmission requestfor UL data) to the eNB 10 using the SRI resource (Processing 1110).

If no SRI resource has been allocated (if “no” in Processing 1109), theUE 20 sends a message #1 to the eNB 10 to perform an RA procedure. Asdescribed above, even when it is determined in Processing 1103 thatsynchronization has been established, in some cases, a RA procedure isperformed if there is no SR PUCCH resource.

In contrast, an RA procedure by the eNB 10 is illustrated in FIG. 4wherein DL data addressed to a UE 20 is arrived at the eNB 10 and the UE20 is notified of the arrival of the DL data by the eNB 10.

More specifically, when DL data addressed to a UE 20 is arrived at theeNB 10 (Processing 1201), the eNB 10 determines, by the ULsynchronization determination unit 14, whether or not UL synchronizationhas been established (Processing 1202 and Processing 1203). If ULsynchronization has not been established yet (if “no” in Processing1203), the eNB 10 notifies the UE 20 of the arrival of the DL data(Processing 1204).

Although an individual preamble may be included in this notification(incoming notification), no individual signature for the UE 20(individual preamble) is not included in this embodiment. Accordingly,the UE 20 that receives the incoming notification will perform acontention-based RA procedure described above. In this case, if a ULresource has been allocated, that UL resource is deallocated and a newUL resource is allocated from the eNB 10 after a successful RA.

In response to receiving the message #1 (RA preamble) from the UE 20that has started the contention-based RA procedure (Processing 1205),the eNB 10 sends a response thereto (message #2) to the UE 20(Processing 1206).

In response to receiving a message #3 from the UE 20 (Processing 1207),the eNB 10 checks whether or not there is any collision of messages(Processing 1208). If not, the eNB 10 sends a message #4 to the UE 20(from the “no” route of Processing 1208 to Processing 1209). If there isa collision of messages (if “yes” in Processing 1208), the eNB 10terminates the RA procedure without sending a message #4.

One fundamental procedure of a contention-based RA is as describedabove. Here, it is assumed that the eNB 10 does not correctly know thevalue of a TA timer 251 in a UE 20 (timer values of the TA timer 151 inthe eNB 10 and the TA timer 251 in the UE 20 are not synchronized).

As an example, let's assume a case in which the TA timer 251 in the UE20 continue to count time, but the eNB 10 misunderstands that the TAtimer 251 in the UE 20 is timed out because the eNB 10 cannot know thatthe TA timer 251 still works.

One example is illustrated in FIG. 5 to FIG. 7 (FIG. 9 to FIG. 11, FIG.13 to FIG. 15, and FIG. 17 to FIG. 19). After performing call settingand UL resource allocation (SRI resource #1, CQI resource #1, SRSresource #1, for example) for the UE 20 (Processing 1008), the eNB 10periodically sends a TA command to the UE 20 (Processing 1009). Inresponse to receiving the TA command (TA value=TA #1; first timingadjustment information), the UE 20 start the TA timer 251.

After the UE 20 performs UL transmission based on TA #1 notified in theTA command and the transmission ends, DL data addressed to the UE 20arrives at the eNB 10. The eNB 10 sends an incoming notification to theUE 20 (sends a message #0) (Processing 1010). In response to theincoming notification #0, the UE 20 starts a contention-based RAprocedure for establishing UL synchronization and reserving resources.

More specifically, the UE 20 sends a message #1 including a selectedsignature (random preamble) to the eNB 10 (Processing 1011). In responseto receiving this message #1, the eNB 10 responds to the UE 20 with anRA response #2 (Processing 1012). At this time, the eNB 10 includes anew TA value (TA #2; second timing adjustment information) in the RAresponse #2.

After receiving the RA response #2, the UE 20 may use the new TA #2 torestart the TA timer 251. However, as described previously, the UE 20may also ignore this TA #2. If the TA #2 is ignored, the TA timer 251may be timed out in somewhere between when sending a message #3 and whenreceiving a message #4 (Processing 1014).

In such a case, the UE 20 determines that synchronization has been lostand deallocates all of reserving UL resource, which makes subsequenttransmissions other than via the RACH impossible.

In this embodiment, UL synchronization and UL resources are maintainedin the following manner if the TA timer 251 is timed out in during acontention-based RA procedure. In the drawings referenced to in thefollowing description (including those for other embodiments describedlater), processing having an identical processing number refers to thesame or similar processing, unless otherwise stated.

(1.4) Case in which no contention with other UE(s) 20 occurs when amessage #4 is received

If there is no contention with other UE(s) 20 (if an RA is successful),an individual UL resource is reserved for the UE 20 that performed theRA. However, since the TA timer 251 is timed out, it is uncertain thatUL synchronization has been established.

Thus, the UE 20 tries to establish UL synchronization using tone of thefollowing four techniques 1-1 to 1-4.

(1.4.1) Technique 1-1 (FIG. 5 to FIG. 8)

As illustrated in FIG. 8, the UE 20 stores, in the memory 252 in thetimer management unit 25, the TA value (TA #2) received in the message#2 during a contention-based RA procedure (Processing 1105 a).

If the UE 20 (the UL resource management unit 26) detects loss of ULsynchronization, the UE 20 can deallocate UL resources that was used intransmission processing based on the TA #1 receive before thecontention-based RA was started (UL resources allocated from the eNB 10before the start of the contention-based RA).

The deallocation may be done when an incoming notification message #0described above is received (when it is recognized that management of ULsynchronization is not out of sync with the eNB 10) (Processing 2001),as illustrated in FIG. 5, or when the TA timer 251 is timed out, asdepicted in FIG. 6 (Processing 2002), for example. As illustrated inFIG. 7, even if the TA timer 251 is timed out, it is possible tomaintain the UL resources (continue to use them), instead ofdeallocating them (Processing 2003).

Thereafter, if the UE 20 continues the contention-based RA procedure andsucceeds in receiving the message #4, the UE 20 applies TA value (TA #2)stored in the memory 252 for the UL transmission and restarts the TAtimer 251 (from the “no” route of Processing 1108 to Processing 1114).

In other words, the application of the TA #2 is allowed once the UE 20receives a message #2 (response signal) containing a T-CRNTI as anexample of identification information of the UE 20 during the RA afterthe TA timer 251 is timed out. Here, the term “application of the TAvalue” means controlling UL transmission (performance of the RA) basedon the transmission timing indicated by TA value. The control may beachieved by one function of the UL synchronization determination unit24, for example (this applied to the embodiments that will bedescribed).

At this time, the value of the TA timer 251 may be a predeterminedvalue, or may be set based on the timing of receiving the message #2.For example, the value of the TA timer 251 may be set by subtracting thetime difference between when the message #2 was received and when themessage #4 was received from a predetermined value, assuming that ULsynchronization has been successfully established at the time when themessage #2 was received. This result in an earlier expiration of timervalue (the valid term of timing adjustment information) by the timedifferent between when the TA #2 is notified in the message #2 and whenthe result of an RA is notified.

As described above, in this embodiment, once receiving the TA #2 duringan RA while the UE 20 is performing the RA to the eNB 10 based on the TA#1, the UE 20 applies the TA #1 to transmission timing adjustment, fortransmission processing until the TA timer 251 is timed out (the validterm of the TA #1 expires). For transmission processing, the TA #2 isapplied to transmission timing adjustment once the TA timer 251 is timedout (the valid term of the TA #1 expires).

Thereby, the TA #2 is applied to perform transmission control after thevalid term of the TA #1 expires (after it is timed out), withoutimmediately updating transmission timing by means of the TA #2.

Thereafter, the UE 20 responds to the eNB 10 with an acknowledgementmessage (ACK or NACK) to the message #4 (Processing 1015). Oncereceiving an ACK as acknowledgement message to the message #4, the eNB10 allocates a new UL resource (SRI resource #2, CQI resource #2, SRSresource #2, for example) to the UE 20 (Processing 1016).

As illustrated in FIG. 7, the UE 20 may continue to use a UL resourcethat has been reserved if not disallocating the UL resource even whenthe TA timer 251 in the UE 20 is timed out. Instead, the UE 20 mayrequest allocation of an alternative UL resource to the eNB 10(Processing 1017).

The UE 20 manages the allocated UL resource in the UL resourcemanagement unit 26, and performs UL transmissions to the eNB 10 usingthat UL resource.

(1.4.2) Technique 1-2 (FIG. 9 to FIG. 12)

In a second technique, a UE 20 stores, in a memory 252, a TA value (TA#2) receive in a message #2, as illustrated in FIG. 9 to FIG. 12(Processing 1105 a). Thereafter, it is assumed that the TA timer 251 istimed out between when a message #3 is send (Processing 1013) and when amessage #4 is received (Processing 1014).

In such a case, the UE 20 applies the TA value (TA #2) stored in thememory 252 to UL transmissions and restarts the TA timer 251, withoutwaiting to receive a message #4 (“yes” route of Processing 1161 toProcessing 1162 in FIG. 12). The restart may be performed at the sametime when the TA timer 251 is timed out. In other words, application ofthe TA #2 receive in the message #2 is allowed at the time when the TAtimer 251 is timed out (the valid term of the TA #1).

Thereby, the TA #2 is applied to perform transmission control at thetime when the valid term of the TA #1 expires (when it is timed out),without immediately updating transmission timing by means of the TA #2.

(1.4.3) Technique 1-3 (FIG. 13 to FIG. 16)

In a third technique, the eNB 10 includes a new TA value (TA #3) whensending a message #4, as illustrated in FIG. 13 to FIG. 16 (Processing1014 a in FIG. 13 to FIG. 15, and Processing 1107 a in FIG. 16).

More specifically, the eNB 10 includes a TA #3 (second transmissiontiming adjustment information) in a message #4 (signal including anS-TMSI as one example of identification information of the UE 20) to besent to the UE 20 during an RA while an UE 20 is performing the RA tothe eNB 10 based on a TA #1 (first transmission timing adjustmentinformation).

In response to receiving the message #4 from the eNB 10, the UE 20applies a TA value (TA #3) included in the message #4 to ULtransmissions and starts the TA timer 251 (Processing 1114 in FIG. 16).

In other words, no TA value is typically included in the message #4including identification information of a user equipment. In thisembodiment, however, by including a TA value in a message #4, a UE 20that ignores a TA #2 receive in a message #2 can apply the TA value inthe message #4 as information for transmission timing adjustment, andstart the TA timer 251.

Note that the UE 20 may store the TA #2 that is ignored in the memory252, in this embodiment.

(1.4.4) Technique 1-4 (FIG. 17 to FIG. 20)

In a fourth technique, a UE 20 restarts the TA timer 251 in response toreceiving a message #2, irregardless whether the UE 20 stores a TA value(TA #2) received in a message #2 from the eNB 10, as illustrated in FIG.17 to FIG. 20.

In this case, the UE 20 can continue to apply a TA value received fromthe eNB 10 (TA #1) in a subsequent RA (UL transmissions) before startinga RA procedure (Processing 1105 b in FIG. 20). In other words, the UE 20can control the TA timer 251 such that the valid term of UL transmissiontiming received in a TA command from the eNB 10 before the RA isstarted, is extended during an RA.

That is, the UE 20 continue to apply the TA #1 without applying a TA #2and extends the valid term of the TA #1 after receiving the TA #2 duringthe RA while performing the RA to the eNB 10 based on the TA #1.

At this time, the extension period (the value of the TA timer 251) maybe a default value, or may be set based on the timing of receiving themessage #2. For example, the value of the TA timer 251 may be set bysubtracting the time difference between when the message #2 is receivedand when the TA #1 is timed out, for UL synchronization.

In accordance with the embodiment, the TA #1 can still be used afterreceiving the a TA #2 and can be applied for transmission timingadjustment.

(1.5) Case in which a contention with other UE(s) 20 occurs when amessage #4 is received

A contention with other UE(s) 20 at the time when a message #4 isreceived means that the same UL resource is also used by the other UE(s)20, and that a unique UL resource cannot be reserved for the localterminal 20.

Therefore, since the UE 20 cannot perform UL data transmission via otherroutes than an RACH, the UE 20 retries to perform a contention-based RAto establish UL synchronization (“yes” route in Processing 1108 in FIG.3).

(2) Second Embodiment

The first embodiment described above assumes the case in which a TAtimer 251 in a UE 20 is timed out until a message #4 is received fromthe eNB 10 after the UE 20 sends a message #3. This embodiment assumesthe case in which a TA timer 251 in a UE 20 is timed out until a message#3 is sent to the eNB 10 after the UE 20 receives a message #2 from theeNB 10.

For example, as illustrated in FIG. 21 to FIG. 23, FIG. 25 to FIG. 27and FIG. 30 to FIG. 32, a contention-based RA (transmission of themessage #1: Processing 1011) is performed once DL data addressed to theUE 20 arrives at the eNB 10 and the UE 20 receives an incomingnotification (Processing 1010). In this case, if the UE 20 that receivesa TA value (TA #2) in the message #2 from the eNB 10 ignores the TA #2,the TA timer 251 may be timed out until a message #3 (signal includingan S-TMSI as one example of identification information of the UE 20) issent.

In such a case, the UE 20 (the UL synchronization determination unit 24)determines that synchronization has been lost, and continues the RAusing one of the following techniques 2-1 to 2-4.

(2.1) Technique 2-1 (FIG. 21 to FIG. 24)

When a UE 20 determines that synchronization has been lost, the UE 20cannot, in principle, transmit a message #3. However, the TA timer 251is often times set within a fail-safe range within which synchronizationon the physical layer is not lost. Accordingly, there may be cases inwhich actual UL synchronization (on a lower layer) is established evenif the TA timer 251 is timed out.

For this reason, in this embodiment, even if a TA timer 251 is timed outafter a UE 20 receives a message #2 from the eNB 10 (Processing 1012),the UE 20 retries to send a message #3 to the eNB 10 (forcedtransmission) (Processing 1013 a in FIG. 21 to FIG. 23, Processing 1105c in FIG. 24, and Processing 1106 a). In other words, even if the timeris timed out, the UE 20 can apply a TA #1 to send a message #3. The TA#2 is stored in the memory 252.

More specifically, the valid term of a TA #1 expires during an RA beforetransmission processing for a message #3 is performed while performingthe RA to the eNB 10 based on the TA #1, the UE 20 can performstransmission processing of the message #3 to the eNB 10 based on the TA#1 even if a TA #2 is received before the expiration of the valid termof the TA #1.

Thereby, the UE 20 can continue the RA procedure without starting acontention-based RA from the beginning, as long as the message #3 isreceived by the eNB 10. In other words, the UE 20 can apply the TA #2 totransmission timing adjustment for future transmission processing andstart the TA timer 251 if the UE 20 succeeds in receiving, as a responsesignal to the message #3, a message #4 containing identificationinformation of the UE 20. Accordingly, it is possible to shorten thedelay until UL data transmission is started.

Since the eNB 10 can recognize that the UE 20 sent the message #3forcefully, the eNB 10 can send a connection rejection message in amessage #4 to the UE 20. More specifically, the eNB 10 can send arejection message to the UE 20 if receiving a message #3 sent from theUE 20 based on the TA #1 after the valid term of the TA #1 expires.

In this case, the UE 20 performs selection or reselection of a cell, orretries an RA procedure. Alternatively, the eNB 10 may not send amessage #4 intentionally. In this case, the UE 20 retries transmissionof a message #3 until an allowable retry count (general maximum retrycount, or a maximum retry count that is exclusively applied to thiscase).

(2.2) Technique 2-2 (FIG. 25 to FIG. 28)

As illustrated in FIG. 25 to FIG. 27, if the TA timer 251 expires beforesending a message #3 to the eNB 10 (Processing 1013) after receiving amessage #2 (TA #2) (Processing 1013), an UE 20 cancels the transmissionof a message #3 and aborts (cancels a contention-based RA procedure thatis being performed (Processing 1018).

In other words, if the valid term of the TA #1 expires during an RAbefore the UE 20 performs transmission processing of a signal includingan S-TMSI as one example of identification information of the UE 20while performing the RA to the eNB 10 based on the TA #1, the UE 20aborts the RA, despite a TA #2 is received before the valid term of theTA #1 expires.

In this case, the UE 20 applies backoff and retries a contention-basedRA, as illustrated in FIG. 28 (“yes” route in Processing 1105 d). Inother words, an RA is retried at the timing based on the backoff time(waiting time period information) received from the eNB 10 during theaborted RA. The UE 20 sends a message #1 (Processing 1011), receives amessage #2 (TA #3) (Processing 1012), and so on, as illustrated in FIG.25 to FIG. 27.

In this flow, the TA timer 251 is timed out (is not started yet) at thetime when the message #2 (TA #2) is received. Accordingly, the UE 20 canapply a new TA #3 that is receive in a message #2 during a retried RA totransmission timing adjustment of subsequent UL transmissions, and startthe TA timer 251. If the UE 20 knows that it is a loser in a RA (acollision occurs) upon receiving a message #4, the TA timer 251 may beforcefully terminated (Processing 2004 in FIG. 25 to FIG. 27).

By aborting an RA procedure and retry an RA when the TA timer 251 istimed out, as in this embodiment, a delay until a UL data transmissionis stated can be shortened than in the case in which the entireremaining procedure (transmission of a message #3 and reception ofmessage #4, for example) is performed.

(2.3) Technique 2-3 (FIG. 25 to FIG. 27, FIG. 29)

If a contention-based RA is retried after the TA timer 251 is timed out,the UE 20 may retry an RA without applying the backoff, as illustratedin FIG. 29 (“yes” route of Processing 1105 d).

In other words, the UE 20 can retry an RA, without applying the backofftime received from the eNB 10 during the aborted RA. Without applyingthe backoff, it is possible to shorten the delay time until a UL datatransmission is started, as compared to the case the backoff is applied.

(2.4) Technique 2-4 (FIG. 30 to FIG. 33)

In addition, as illustrated in FIG. 30 to FIG. 32, when the TA timer 251is timed out, the UE 20 may notify an upper layer (for example, an RRClayer), irrespective whether the backoff is applied (Processing 1021,the “yes” route of Processing 1105 d to Processing 1113 in FIG. 33).

This enable the upper layer of the UE 20 to start a monitor timer of anRA and monitor whether the RA procedure is continued (retried). In otherwords, the UE 20 monitors the RA whether the TA timer 251 is timed out(whether the valid term of the TA #1 expires). In response to themonitor timer being timed out during the RA, the upper layer of the UE20 performs a cell selection or cell reselection processing (Processing1022 in FIG. 30 to FIG. 32).

Accordingly, the UE 20 can initiate an RA with another cell (eNB 10)earlier, and it is possible to reduce the time delay until a UL datatransmission is started. Note that monitor of an RA by the upper layerwhether the TA timer 251 is timed out may also be used in theabove-described techniques 2-1 to 2-3.

(3) Third Embodiment

Next, this embodiment assumes the case in which the eNB 10 can correctlymanage the timer value of a TA timer 251 in a UE 20 (the TA timers 151and 251 of the eNB 10 and the UE 20 are synchronized). In this case,since the eNB 10 can recognize that the TA timer 251 in the UE 20 stillworks, the UE 20 can trust the TA value received from the eNB 10. Inaddition, unlike in the first and second embodiments, a TA value may beadvantageously sent from the eNB 10.

In response to arrival of DL data addressed to a UE 20 at the eNB 10after the UE 20 completes to send UL data based on the TA value receivein the TA command, the eNB 10 sends an incoming notification to the UE20 (sends a message #0).

Thereby, the UE 20 receiving the incoming notification starts acontention-based RA procedure. Thereafter, if the TA timer 251 in the UE20 is timed out between when a message #2 is received (Processing 1012)and when a message #3 is sent (Processing 1013), the UE 20 tries toestablish UL synchronization using tone of the following four techniques3-1 to 3-3.

(3.1) Technique 3-1

Similar to the technique 1-2 (FIG. 9 to FIG. 12) that has been describedwith reference to the first embodiment, an UE 20 stores, in the memory252, a TA value received from the eNB 10 in a the message #2 during anRA procedure. When the TA timer 251 is timed out before sending a themessage #3 to the eNB 10, the UE 20 applies the TA value stored in thememory 252 to UL transmission, and starts the TA timer 251.

(3.2) Technique 3-2

An UE 20 performs one of the techniques 2-1 to 2-4 that have beendescribed with reference to the second embodiment.

(3.3) Technique 3-3 (FIG. 34 to FIG. 37)

As illustrated in FIG. 34 and FIG. 35, a UE 20 sends a signal (themessage #3) including an S-TMSI as one example of identificationinformation of the UE 20 during an RA while performing the RA to the eNB10 based on the TA #1 (Processing 1013).

In response to receiving the message #3 from the UE 20 RA before the TAtimer 251 in the UE 20 is timed out (Processing 1013), the eNB 10 sendsa TA command including a new TA value (TA #3; second timing adjustmentinformation) to the UE 20 (Processing 1009 a, Processing 1208 a in FIG.36).

The UE 20 monitors (polls) whether a TA command is received even duringexecution of the RA. For example, the UE 20 monitors whether a TAcommand is received from the eNB 10 after sending the message #3 to theeNB 10 (Processing 1013). In response to receiving a TA command from theeNB 10 while monitoring (Processing 1009 a, and Processing 1161 in FIG.37), the UE 20 (the timer management unit 25) applies the TA value (TA#3) of the receive TA command to UL transmission, and starts the TAtimer 251 (Processing 1162 in FIG. 37).

Note that UL resources are managed by the UE 20 in the manner similar tothat of the first or second embodiment. For example, UL resources thathave been reserved may be deallocated when incoming notification (themessage #0) of DL data is received from the eNB 10, or when the TA timer251 is timed out. In addition, even if the TA timer 251 is timed outbefore the TA #3 is received (when the valid term of the TA #1 isreached), it is also possible to maintain the UL resources that havebeen reserved (continue to use them), rather than deallocating them(Processing 2005 in FIG. 35).

In addition, the UE 20 can apply the same technique as in the firstembodiment (one of the technique 1-1 to technique 1-4) when the TA timeris timed out between when sending a message #3 and when receiving amessage #4.

Various inconveniences, which may occur during adjusting transmissiontiming from a base station to a terminal (user equipment), can besolved.

The delay time until a user equipment can initiate a communication afterconnecting to a base station can also be reduced.

All examples and conditional language recited herein are intended forpedagogical purposes to aid the reader in understanding the inventionand the concepts contributed by the inventor to furthering the art, andare to be construed as being without limitation to such specificallyrecited examples and conditions, nor does the organization of suchexamples in the specification relate to a showing of the superiority andinferiority of the invention. Although the embodiment(s) of the presentinvention has(have) been described in detail, it should be understoodthat the various changes, substitutions, and alterations could be madehereto without departing from the spirit and scope of the invention.

What is claimed is:
 1. A mobile communication system having userequipment that performs transmission process having transmission timingadjustment information and a base station that receives a signal sentfrom the user equipment, the mobile communication system comprising:when, during a connection process, a timer that is in accordance withfirst transmission timing adjustment information expires before the userequipment transmits a signal that includes identification information ofthe user equipment, the user equipment does not transmit the signal thatincludes the identification information of the user equipment, whereinthe connection process includes reception of second transmission timingadjustment information while the user equipment contains the firsttransmission timing adjustment information, wherein the connectionprocess connects the user equipment to the base station.
 2. The mobilecommunication system according to claim 1, wherein the user equipmentdoes not transmit the signal, if the timer in accordance with the firsttransmission timing adjustment information expires before transmissionof the signal including the identification information of the userequipment and after reception of the second transmission timingadjustment information by the user equipment during the connectionprocess while the user equipment has the first transmission timingadjustment information and performs the connection process to the basestation.
 3. A user equipment in a mobile communication system having theuser equipment and a base station that receives a signal sent from theuser equipment, the user equipment comprising: a transmitter configuredto perform a transmission process on the base station based ontransmission timing adjustment information; and a processor configuredto: execute a connection process that connects to the base station; andwhen a timer that is in accordance with first transmission timingadjustment information expires before the user equipment transmits asignal that includes identification information of the user equipment,not transmit the signal that includes the identification information ofthe user equipment, wherein the connection process includes reception ofsecond transmission timing adjustment information while containing thefirst transmission timing adjustment information.
 4. A base station forreceiving a signal sent from the user equipment as claimed in claim 3.5. A timing adjustment method in a mobile communication system havinguser equipment that performs a transmission process based ontransmission timing adjustment information and a base station thatreceives a signal sent from the user equipment, the timing adjustmentmethod comprising: when, during a connection process, a timer that is inaccordance with first transmission timing adjustment information expiresbefore the user equipment transmits a signal that includesidentification information of the user equipment, not transmitting thesignal that includes the identification information of the userequipment, wherein the connection process includes reception of secondtransmission timing adjustment information while the user equipmentcontains the first transmission timing adjustment information, whereinthe connection process connects the user equipment to the base station.